1. Field of the Invention
The present invention relates to an apparatus for reducing the effort and force required to place and hold a medical instrument on or against a patient. The present invention may be used in performing ultrasound examinations. The present invention includes an equipoising arm structure that can selectively exert force in any direction—lifting, pressing down, or applying lateral bias—with consistent force throughout its range of articulation.
2. Background of the Present Invention
The placement of a medical device on or against the skin of a patient typically requires physical exertion by the operator or medical practitioner. Such medical devices have their own weight and are often attached to cumbersome wires or tubes. Medical practitioners face further physical challenge due to the need to firmly press the medical device against the skin of a patient for extended periods of time.
Ultrasound examinations require direct skin contact with a medical instrument and the application of steady force against the skin of a patient. Different patients require different directions and magnitudes of applied force during an ultrasound examination. For example, a prone pregnant woman or obese patient will require the mild application of downward and lateral pressure to fully cover the abdominal area. On the other hand, a shoulder examination for a patient sitting upright may require firm side pressure or pressure perpendicular to the Earth's gravity.
Many medical devices, such as transducers used in ultrasound examinations, are coated in a jelly type material and are then pressed against the skin of a patient. With the use of such jelly, the patient's skin presents a slippery, moving, and sometimes squirming surface. The medical practitioner is then faced with the physical challenge of pressing and systematically moving the medical device on a three dimensional surface that is slippery, moving, and breathing.
Many medical practitioners experience muscle fatigue and injury as a result of the physical exertion required in performing ultrasound examinations or similar examinations with other medical devices. Thus, there is an urgent need in the art for means to reduce the physical effort expended by medical practitioners in performing ultrasound examinations or similar procedures.
Robotic arms are known in the related art and are used in many industries to perform automated tasks or to reduce human physical effort. Most medical procedures do not lend themselves to the use of typical industrial robots or mechanical arms. Most medical procedures require a skilled, delicate, human directed touch to be effective and to be accepted by patients. For example, a pregnant woman might only reluctantly consent to an ultrasound examination performed with a large or computer controlled robotic arm.
There is a need in the art for means to allow hand placement and hand controlled pressure of medical devices on or against patients while reducing muscle fatigue and injury to medical practitioners. There is a need in the art for non-obtrusive means to amplify the force used by medical practitioners in manipulating medical devices.
Spring powered ‘equipoising’ parallelogram arms have been used for decades to support and position medical payloads such as x-ray machines and dental equipment. These arms rely to a greater or lesser extent on friction to retain a set angle or position, since existing spring geometries do not necessarily provide appropriate or consistent lift throughout the entire angular excursion of the parallelogram links. The invention of the articulated, force-exerting arms marketed under the trademark Steadicam®, however, has provided nearly frictionless support of a floating camera payloads in order to isolate them from unwanted spatial movements of camera operators, employing a spring design for the support arm that ‘equipoises’ the payload, countering the fixed weight of the gimbaled camera assembly with nearly constant positive buoyancy from its lowest to its highest point of parallelogram articulation.
The formulas for determining the appropriate spring rate to achieve equipoise factor down to the expression K=P/d, where K is the spring rate, P is the load and d is the height of the lifting triangle which is incorporated into the parallelogram and exercises it upward. When a spring of the rate specified in the above formula is deployed as the third side of the triangle, it produces the appropriate force to exactly lift the specified weight throughout the entire vertical range of articulation. This property is termed “iso-elasticity”.
U.S. Pat. No. 5,360,196 and continuation U.S. Pat. No. 5,435,515 (incorporated herein by reference), disclose adjusting the lifting strength of the arm in a novel manner by raising and lowering the effective spring attachment point along a path angularly offset from the adjacent vertical link of the parallelogram (thus increasing or decreasing the height and also the efficiency of the lifting triangle) without compromising the spring rate required to provide ‘iso-elasticity’. The same formula, K=P/d, indicates that if the height of the appropriate lifting triangle is increased or reduced proportionately with the weight to be carried, the property of iso-elasticity will be maintained.
However, there is a need in the art for means to push down and/or laterally rather than just lift up, in order to reduce the physical effort exerted by medical professionals in performing ultrasound examinations and still maintain the “hands on” skill and patient comfort provided by a human being.